Antenna device and portable machine

ABSTRACT

An antenna device includes: a conductive board ( 3 ) having one end portion and the other end portion opposite the one end portion; a flat plate antenna( 4, 18   a,    18   b,    19 ) mounted on the board ( 3 ) with a dielectric interposing therebetween wherein when feeding a current thereto to excite, a current also flows in said board ( 3 ); a first current direction change means ( 5   a,    6, 6   a,    6   c,    7, 7   a,    7   c,    14   a,    17   a,    17   c,    21   a,    22   a,    22   b,    24   a ) changing a direction of the current flowing in the board ( 3 ) to a first direction when exciting the antenna ( 4, 18   a,    18   b,    19 ) and located on said one end portion of the board ( 3 ); and a second current direction change means ( 5   b,    6, 6   b,    6   d,    7, 7   b,    7   d,    14   b,    17   b,    17   d,    21   b,    22   c,    22   d,    24   b ) changing a direction of the current flowing in the board ( 3 ) to a second direction different from the first direction when exciting said antenna ( 4, 18   a,    18   b,    19 ) and located on the other end portion of the board ( 3 ).

TECHNICAL FIELD

The present invention relates to an antenna device and portableequipment, and more particularly, to an antenna device and portableequipment capable of reducing a size and weight thereof.

BACKGROUND ART

In recent years, a portable telephone has been widely spread. In mobilecommunication to use this portable telephone or the like, transmissionwaves are subjected to multi-reflection or scattering caused bybuildings or the like present between a portable telephone as a mobilestation and a base station. For this reason, polarization fluctuation ofradio waves and others occur, resulting in level fluctuation of areceived signal in a portable telephone and in turn, in deterioration incommunication quality. In order to alleviate such deterioration incommunication quality, there has been employed the diversity receptionin which radio waves are received using two antennae and receivedsignals through the antennae are synthesized or one thereof at a higherlevel is selected, thereby alleviating an influence of level fluctuationon a received signal.

FIG. 14 is a view showing a conventional portable telephone in asimplified manner. Description will be given of the conventionalportable telephone with reference to FIG. 14.

Referring to FIG. 14, a portable telephone 101 adopts a so-called spacediversity reception scheme as a measure to alleviate the deteriorationin communication quality, including: two antennae of a whip antenna 150;and a built-in antenna 151 such as a flat plate antenna mounted inside acase of portable telephone 101.

In portable telephone 101 shown in FIG. 14, since antenna 150 andbuilt-in antenna 151 for transmitting/receiving radio waves in the sameband are installed adjacent to each other, a problem has been arisenthat antenna 150 and built-in antenna 151 are electromagneticallycoupled with each other to deteriorate an efficiency of the antenna.

Furthermore, as another type of the diversity reception, there has alsobeen known a so-called polarization diversity reception scheme using apatch antenna. FIGS. 15 and 16 are model diagrams each showing anantenna device adopting a polarization diversity reception scheme.

Referring to FIG. 15, a patch antenna 152 is mounted on a board 103.Feed points 105 a and 105 b connected to a feed source are provided onadjacent sides of the periphery of patch antenna 152. By switchingbetween feed points 105 a and 105 b, a plane of polarization of thepatch antenna can be changed over from one of two directions indicatedby two arrow marks 153 and 154 to the other. Moreover, as shown in FIG.16, in the patch antenna 152, by switching between ground points 114 aand 114 b instead of feed points, switching between planes ofpolarization can also be realized. Referring to FIG. 16, ground points114 a and 114 b grounding patch antenna 152 to the board are provided onadjacent side of a periphery of patch antenna 152. Furthermore, a feedpoint 105 connected to a feed source is provided on patch antenna 152.

Since such a patch antenna has a large antenna size, however, it, as wasin the prior art, has been hard to be applied to portable equipment suchas a portable telephone requiring reduction in size and weight.

As described above, in portable equipment such as a portable telephonerequiring reduction in size and weight, it has been hard to suppressdeterioration in communication quality without reducing an efficiency ofan antenna.

The present invention has been made in order to solve such a problem andit is an object of the present invention to provide an antenna deviceand portable equipment capable of reducing a size and weight thereof andpreventing deterioration in communication quality to be otherwise causedby polarization fluctuation of a radio wave and others withoutdecreasing an antenna efficiency.

DISCLOSURE OF THE INVENTION

An antenna device in a first aspect of the present invention includes: aconductive board having one end portion and the other end portionopposite the one end portion; a flat plate antenna; first currentdirection change means; and second current direction change means. Theflat plate antenna is mounted on the board with a dielectric interposingtherebetween and when feeding a current thereto to excite, a currentalso flows in the board. The first current direction change meanschanges a direction of the current flowing in the board to a firstdirection when exciting said antenna and located on the one end portionof the board. The second current direction change means changes adirection of the current flowing in the board to a second directiondifferent from the first direction when exciting the antenna and locatedon the other end portion of the board.

With such a construction adopted, directions of a strength of a radiowave radiated from the antenna device including the antenna and theboard can be changed therebetween in respective cases where a directionof a current flowing in the board is the first direction and where adirection of a current flowing in the board is the second direction.That is, the directivity of the antenna can be changed. Here, the firstdirection is, for example, a direction along a diagonal line extendingfrom the one end portion of the board to the opposite corner of theboard and the second direction is exemplified as a direction along adiagonal line extending from the other end portion of the board to theopposite corner of the board. Furthermore, since a direction of thecurrent flowing in the board is different according to the firstdirection or the second direction, a main polarization direction of theantenna device in each of the respective cases is different from that inthe other cases. That is, by changing a direction of current flowing inthe board from the first direction to the second direction and viceversa, directivity and a polarization direction of the antenna devicecan be changed. Therefore, an antenna device can be realized thatoperates as if it had two antennae different in directivity andpolarization from each other using one antenna. As a result, thediversity reception can be implemented using one antenna. Accordingly,since no necessity arises for two antennas, which was required in aconventional practice, thereby preventing from occurrence of a problemof electromagnetic coupling between two antennas.

Furthermore, since functions of two antennas are realized with oneantenna, a size and weight of an antenna device can be reduced comparedwith those in a case where two separate antennas are installed.

In the antenna device according to the above first aspect, the antennamay be installed so as to extend from a position on the one end portionof the board to a position on the other end portion of the board. Thefirst current direction change means may include first feed means, whichis connected to one portion of the antenna located on the one endportion of the board, for exciting the antenna and first feed controlmeans for controlling feed of a current to the antenna from the firstfeed means. The second current direction change means may include secondfeed means, which is connected to another portion of the antenna locatedon the other end portion of the board, for exciting the antenna andsecond feed control means for controlling feed of a current to theantenna from the second feed means.

In this case, by switching between the first and second feed means usingthe first and second feed control means, a position of a feed point ofthe antenna can be changed over from a position in the one portion ofthe antenna to a position in the second portion of the antenna. Byswitching between positions of feed points in this way, a direction ofthe current flowing in the board can be easily changed over from thefirst direction to the second direction and vice versa. As a result,since an antenna device can be realized that operates as if it had twoantennas different in directivity and polarization from each other usingone antenna, the diversity reception can be realized using one antenna.

The antenna device according to the above first aspect may furtherinclude feed means for exciting the antenna. The antenna may beinstalled so as to extend from a position on the one end portion of theboard to a position on the other end opposite the one end portion of theboard. The first current direction change means may include a firstground means electrically connecting one portion of the antenna locatedon the one end portion of the board with the one end portion of theboard and a first ground control means controlling connection of thefirst ground means with the antenna. The second current direction changemeans may include a second ground means electrically connecting a secondportion of the antenna located on the other end portion of the boardwith the other end portion of the board and a second ground controlmeans controlling connection of the second ground means with theantenna.

In this case, by switching between the first and second ground means, aposition of a ground point of the antenna can be changed over from aposition in the one portion of the antenna to a position in the secondportion of the antenna. By switching between positions of the groundpoints in this way, a direction of the current flowing in the board canbe easily changed over from the first direction to the second directionand vice versa. As a result, since an antenna device can be realizedthat operates as if it had two antennas different in directivity andpolarization from each other using one antenna, the diversity receptioncan be realized using one antenna.

In the antenna device according to the above first aspect, the feedmeans is preferably connected to the central portion of the antenna; inthe first ground means, the one end portion of the board is preferablyconnected to the one portion of the antenna at a first ground point ofthe one portion of the antenna; and in the second ground means, theother end portion of the board is preferably connected to the secondportion of the antenna at a second ground point of the second portion ofthe antenna. The first ground point and the second ground point arepreferably located at positions in bilateral symmetry with respect tothe central portion of the antenna.

In this case, since the first and the second ground points arepreferably located positions in bilateral symmetry with respect to thecentral portion of the antenna, common feed means for the first andsecond ground points can be provided at the central portion of theantenna. As a result, a construction of the antenna device can besimplified as compared with that in a case where two feed meanscorresponding to the first and second ground points are provided in anantenna device.

In the antenna device according to the above first aspect, the antennamay be installed so as to extend from a position on the one end portionof the board to a position on the other end portion opposite the one endportion of the board, and the first current direction change means mayinclude: a first ground means electrically connecting one portion of theantenna located on the one end portion of the board to the one endportion of the board; a first feed means, connected to the one portionof the antenna located on the one end portion of the board, and forexciting the antenna; and a first feed ground control means switchingbetween the first ground means and the first feed means. The secondcurrent direction change means may include: a second ground meanselectrically connecting a second portion of the antenna located on theother end portion of the board to the other end portion of the board; asecond feed means, connected to the second portion of the antennalocated on the other end portion of the board, and for exciting theantenna; and a second feed ground control means switching between thesecond ground means and the second feed means.

In this case, by controlling the first and second feed ground controlmeans, a feed point and a ground point of the antenna can be arbitrarilyprovided in one of a region located on the one end portion of the boardand a region located on the other end portion of the board. By switchingbetween positions of a ground point and a feed point in this way, adirection of the current flowing in the board can be easily changed overfrom the first direction to the second direction and vice versa. As aresult, since an antenna device can be realized that operates as if ithad two antennas different in directivity and polarization from eachother using one antenna, the diversity reception can be realized usingone antenna.

In the antenna device according to the above first aspect, an electricallength of the antenna is preferably substantially ¼ times a wavelengthof a radio wave that can be received by the antenna.

In this case, a so-called λ/4-wave antenna (λ indicates a wavelength ofa radio wave) is advantageous in reducing its size and by using such anantenna, further reduction in size and weight of an antenna device canbe realized.

In the antenna device according to the above first aspect, the antennapreferably includes a first element capable of receiving a radio wavehaving a first frequency; and a second element capable of receiving aradio wave having a second frequency different from the first frequency.

In this case, by applying the present invention in a multi-frequencyantenna device including the first and second elements, a direction of acurrent flowing in the board can be changed over from the firstdirection to the second direction and vice versa. Thereby, directivityand a polarization direction of an antenna device can be changed. Thatis, since one multi-frequency antenna can operates as if it were twoantennas different in directivity and polarization from each other, thediversity reception can be easily realized using one multi-frequencyantenna.

In the antenna device according to the above first aspect, the firstcurrent direction change means may include: a first feed source feedinga current having a first frequency for exciting the antenna; a secondfeed source feeding a current having a second frequency different fromthe first frequency for exciting the antenna; a first filtertransmitting a current having the first frequency; and a second filtertransmitting a current having the second frequency. The first feedsource may be connected to a first common connection point of theantenna through the first filter, and the second feed source may beconnected to the first common connection point of the antenna throughthe second filter. The second current direction change means mayinclude: a third feed source feeding a current having the firstfrequency for exciting the antenna; a fourth feed source feeding acurrent having the second frequency different from the first frequencyfor exciting the antenna; a third filter transmitting a current havingthe first frequency; and a fourth filter transmitting a current havingthe second frequency. The third feed source may be connected to a secondcommon connection point of the antenna through the third filter, and thefourth feed source may be connected to the second common connectionpoint of the antenna through the fourth filter.

In this case, with the first and second filters used, the first andsecond feed source feeding currents having respective differentfrequencies can be connected to the first common connection point of theantenna. Furthermore, with the third and fourth filters used, the thirdand fourth feed source feeding currents having respective differentfrequencies can be connected to the second common connection point ofthe antenna. That is, since plural feed sources can be connected to theantenna by one connection point, the number of connection points of feedsources to the antenna can be reduced. As a result, a construction ofthe antenna can be simplified. Hence, the antenna device can be reducedin size and weight.

In the antenna device according to the above first aspect, the antennamay include a part having a function as a conductive wire for a currentfed to the antenna and a function as a matching element.

In this case, since no necessity arises for installment of a separatematching element in addition to the antenna, a simpler construction ofthe antenna device can be realized. Hence, the antenna device can bereduced in size and weight.

In the antenna device according to the above first aspect, the firstcurrent direction change means may includes: a first matching circuitmember; and a first feed means electrically connected to the antennathrough the first matching circuit member, and the second currentdirection change means may include: a second matching circuit member;and second feed means electrically connected to the antenna through thesecond matching circuit member.

In this case, with the first and second matching circuits used, acharacteristic of the antenna can be finely adjusted.

Portable equipment in another aspect is provided with the antenna deviceaccording to the first aspect.

With such construction adopted, since one antenna device can operate asif it were two antennas different in directivity and polarization fromeach other, reduction in size and weight of portable equipment can beachieved compared with an antennas device in a case where two antennasare actually installed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a model diagram showing a first embodiment of a portabletelephone according to the present invention;

FIG. 2 is a model diagram showing a second embodiment of a portabletelephone according to the present invention;

FIG. 3 is a model diagram showing a third embodiment of a portabletelephone according to the present invention;

FIG. 4 is a model diagram showing a fourth embodiment of a portabletelephone according to the present invention;

FIG. 5 is a model diagram showing a fifth embodiment of a portabletelephone according to the present invention;

FIG. 6 is a model diagram showing a sixth embodiment of a portabletelephone according to the present invention;

FIG. 7 is a model diagram showing a seventh embodiment of a portabletelephone according to the present invention;

FIG. 8 is a model diagram showing a board and an antenna constituting anantenna device of a portable telephone used in a test;

FIG. 9 is an illustration showing a process measuring a radiationpattern in an X-Z plane shown in FIG. 8;

FIG. 10 is an illustration showing a process measuring a radiationpattern in an X-Z plane shown in FIG. 8;

FIG. 11 is an illustration showing a process measuring a radiationpattern in an X-Z plane shown in FIG. 8;

FIG. 12 is a graph showing a radiation pattern when a flat plate antenna4 is fed from a feed point 24 a in FIG. 8;

FIG. 13 is a graph showing a radiation pattern when flat plate antenna 4is fed from a feed point 24 b in FIG. 8;

FIG. 14 is a model diagram showing a conventional portable telephone;

FIG. 15 is a model diagram showing an antenna device adopting apolarization diversity reception scheme; and

FIG. 16 is a model diagram showing an antenna device adopting apolarization diversity reception scheme.

BEST MODE FOR CARRYING OUT THE INVENTION

Description will be given of embodiments of the present invention belowwith reference to the accompanying drawings. Note that in the followingdrawings, the same or corresponding constituents are attached by thesame reference numerals and none of descriptions thereof is repeated.

(First Embodiment)

Description will be given of a first embodiment according to the presentinvention with the reference to FIG. 1.

Referring to FIG. 1, a portable telephone 1 includes: a case 2constituting a body; a conductive board 3 mounted inside case 2; and aflat plate antenna 4 installed on board 3 with a clearance therebetween.A ground point, though not shown, electrically connected to board 3 isprovided to flat plate antenna 4. Feed points 5 a and 5 b are providedat both end portions of flat plate antenna 4. Feed point 5 a provided atone end portion as one portion of flat plate antenna 4 is electricallyconnected to a terminal 8 a on a change-over switch 7 by a conductivewire. Feed point 5 b provided at the other end portion as anotherportion of flat plate antenna 4 is electrically connected to a terminal8 b provided on change-over switch 7. A terminal 8 c on change-overswitch 7 is electrically connected to a feed source 6 by a conductivewire. By electrically connecting terminal 8 c to which feed source 6 isconnected to one of terminals 8 a and 8 c using a conductive wire 9 orthe like, a current for exciting flat plate antenna 4 can be fed theretofrom one of two feed points 5 a and 5 b of flat plate antenna 4. Thatis, with change-over switch 7 provided, feed of a current from feedsource 6 to flat plate antenna 4 through feed points 5 a and 5 b can beON/OFF controlled. Here, flat plate antenna 4 is a quarter wavelengthantenna (an antenna of a λ/4 type, wherein λ indicates a wavelength of aradio wave) and for example, when terminals 8 a and 8 c are connected toeach other to feed a current from feed point 5 a to flat plate antenna4, the current flows in a direction (a direction along a diagonal lineextending from the one end portion of board 3 to the opposite cornerthereof) shown with a dotted line 10 as a first direction in board 3electrically connected to flat antenna 4. Directivity of antenna 4 whena current flows as shown with the dotted line 10 is simply indicatedwith a dotted line 11. Moreover, when terminals 8 b and 8 c areconnected to each other to feed a current from feed point 5 b to flatplate antenna 4, the current flows in a direction (a direction along adiagonal line extending from the other end portion of board 3 to theopposite corner thereof) shown with a solid line 12 as a seconddirection in board 3 electrically connected to flat antenna 4.Directivity of antenna 4 when a current flows as shown with solid line12 is simply indicated with a solid line 13.

In such a manner, directions of a strength of a radio wave can bechanged over therebetween in respective cases where a direction of thecurrent flowing in board 3 is a direction shown dotted line 10 as thefirst direction and where the direction of the current is a directionshown with solid line 12 as the second direction. That is, directivityof an antenna device can be changed.

Further, since directions of a current flowing in the board aredifferent from each other in the respective cases of the first directionshown with dotted line 10 and the second direction shown with the solidline 12, polarization directions of the antenna device in both cases aredifferent from each other. Therefore, by selecting the first directionor second direction, both being different from each other as a directionof the current flowing in board 3, directivity and a polarizationdirection of the antenna device can be changed. For this reason,portable telephone 1 equipped with an antenna device can be realizedthat operates as if it had two antennas different in directivity andpolarization from each other using one flat plate antenna 4. As aresult, a diversity reception scheme can be realized using one flatplate antenna 4. Therefore, since two antennas, which were required in aprior art, are not required, thereby preventing from occurrence of aproblem of electromagnetic coupling between two antennas.

Furthermore, since functions of two antennas are realized using one flatplate antenna 4, portable telephone 1 can be smaller and lighter than ina case of portable telephone equipped with two separate antennas.

In addition, by switching between feed points 5 a and 5 b connected tofeed source 6 using change-over switch 7 as first and second feedcontrol means, positions of a feed point can be changed overtherebetween in respective end portions of flat plate antenna 4(change-over from the one portion to the second portion of flat plateantenna 4). In such a way, by connecting one of feed points 5 a and 5 bto feed source 6 to act as a feed point feeding a current to flat plateantenna 4, change-over can be easily performed between the firstdirection (a direction shown with dotted line 10) and the seconddirection (a direction shown with solid line 12) of the current flowingin board 3.

Moreover, since a so-called λ/4 antenna as shown in FIG. 1 is small insize, portable telephone 1 can be realized in a smaller and lighterform. Note that as an antenna used in the present invention, there canbe used antennas other than the so-called above λ/4 antenna, such as a3λ/8 antenna.

(Second Embodiment)

Description will be given of a second embodiment of a portable telephoneaccording to the present invention with the reference to FIG. 2.

Referring to FIG. 2, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 1. Inportable telephone 1 shown in FIG. 2, however, a ground point 14 a isprovided at one end portion as one portion of a flat plate antenna 4,and a ground point 14 b is provided at the other end portion as a secondportion. Furthermore, a feed point 5 electrically connected to a feedsource 6 is provided in the central portion of flat plate antenna 4.Ground point 14 a is electrically connected to a terminal 8 d on achange-over switch 7 a by a conductive wire. Besides, a terminal 8 egrounded to a board 3 is provided on change-over switch 7 a. Terminals 8d and 8e are connected to each other using a conducting wire 9 or thelike, or alternatively are placed in an open state without connectingterminals 8 d and 8 e therebetween, thereby enabling control on thepresence or absence of grounding to board 3 at ground point 14 a of flatplate antenna 4 (a state, open or closed, in grounding flat plateantenna 4 to board 3).

Furthermore, a ground point 14 b provided at the other end portion offlat plate antenna 4 is connected to a terminal 8 f provided on achange-over switch 7 b by a conductive wire. Moreover, a terminal 8 ggrounded to board 3 is provided on change-over switch 7 b. Terminals 8 fand 8 g are electrically connected to each other by conductive wire 9 orthe like, or alternatively are placed in an open state withoutconnecting terminals 8 f and 8 g therebetween, by which change-overoperation control is enabled on the presence or absence of grounding toboard 3 at ground point 14 b of flat plate antenna 4. By changing overfrom an operation connecting terminals 8 d and 8 e therebetween to anoperation disconnecting terminals 8 f and 8 g from each other and viceversa at change-over switches 7 a and 7 b, respectively, only one ofground points 14 a and 14 b of flat plate antenna 4 can be placed in astate of being connected to board 3.

In a case where while terminals 8 d and 8 e of change-over switch 7 aare connected to each other by conductive wire 9, terminals 8 f and 8 gof change-over switch 7 b are, on the other hand, not connected to eachother (in an open state), thereby grounding ground point 14 a to board3, a current flows in a direction indicated by a dotted line 15 in board3 upon exciting of flat plate antenna 4. Furthermore, in a case wherewhile terminals 8 d and 8 e of change-over switch 7 a assume an openstate, terminals 8 f and 8 g of change-over switch 7 b are, on the otherhand, connected to each other by conductive wire 9, thereby groundingground point 14 b to board 3, a current flows in a direction indicatedby a solid line 16 in board 3.

By selectively using ground point 14 a or 14 b to change over betweenground points of flat plate antenna 4, directions of a current flowingin board 3 can be changed with ease, similar to the portable telephoneaccording to the first embodiment of the present invention. As a result,there can be obtained an effect similar to the first embodiment of aportable telephone according to the present invention.

Furthermore, as shown in FIG. 2, since ground points 14 a and 14 b arelocated in bilateral symmetry with respect the central portion of flatplate antenna 4, feed means 5 shared between ground points 14 a and 14 bcan be provided at the central portion of flat plate antenna 4. As aresult, a construction of telephone 1 can be simpler than in a casewhere two feed points are provided in correspondence to two groundpoints 14 a and 14 b in flat plate antenna 4 of portable telephone 1.

(Third Embodiment)

Description will be given of a third embodiment of a portable telephoneaccording to the present invention with reference to FIG. 3.

Referring to FIG. 3, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 2.However, feed/ground terminals 17 a and 17 b to play roles both of afeed point and a ground point are provided at both end portions of aflat plate antenna 4. Feed/ground point 17 a is electrically connectedto a terminal 8 i provided on a change-over switch 7 a by a conductivewire or the like. In addition, a terminal 8 h electrically connected toa feed source 6 and a terminal 8 j grounded to one end portion of aboard 3 are provided to change-over switch 7 a. Terminal 8 i and each ofterminals 8 h and 8 j are connectable therebetween by a conductive wireor the like. Terminal 8 i can be electrically connected to one ofterminals 8 h and 8 j by changing over between terminals 8 h and 8 j.

Feed/ground point 17 b disposed in the other end portion of flat plateantenna is electrically connected to a terminal 8 l provided on achange-over switch 7 b by a conductive wire or the like. A terminal 8 kelectrically connected to feed source 6 and a terminal 8 m grounded tothe other end portion of board 3 are provided to change-over switch 7 b.Switching is enabled between electrical connections of terminal 8 l witheach of terminals 8 m and 8 k.

In this case, by controlling change-over switches 7 a and 7 b as firstand second feed ground control means, a feed point and a ground point offlat plate antenna 4 can be arbitrarily set at any of a region locatedon the one end portion of board and a region located on the other endportion on board. By switching between a ground point and a feed pointin flat plate antenna 4, a direction of a current flowing in board 3 canbe easily changed, similarly to the first and second embodiments of thepresent invention. There can be achieved an effect similar to a portabletelephone in any of the first and second embodiments of the presentinvention.

(Fourth Embodiment)

Description will be given of a fourth embodiment of a portable telephoneaccording to the present invention with reference to FIG. 4.

Referring to FIG. 4, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 3.However, in portable telephone shown in FIG. 4, an antenna includes: aresonance element 18 a adapted to a radio wave having a first frequency;a resonance element 18 b adapted to a radio wave having a secondfrequency different from the first frequency; and an antenna element 19,electrically connected to resonance elements 18 a and 18 b, playing bothrolls of a feed line as a conductive wire and a short stub as a matchingelement. With such a construction, since no necessity arises forinstallment of a separate matching element in addition to the antenna inportable telephone 1, a construction of portable telephone 1 can besimplified. Therefore, there can be achieved reduction in size andweight of portable telephone 1.

Feed/ground points 17 c and 17 d are provided at both end portions ofantenna element 19. Feed/ground point 17 c is electrically connected toa terminal 8 i on a switch 7 a, and feed/ground point 17 d iselectrically connected to a terminal 8 l on a switch 7 b. By controllingchange-over switches 17 a and 17 b, feed/ground points 17 a and 17 b ofthe antenna can be acted as a feed point or a ground point (switchingbetween feed points or ground points). As a result, a direction of thecurrent flowing in a board 3 can be changed, similar to the thirdembodiment of the present invention.

In such a way, since even in a multi-frequency antenna device includingresonance elements 18 a and 18 b as first and second elements, adirection of a current flowing in board 3 can be changed, directivityand a polarization direction of portable telephone 1 can be changed.Therefore, there can be attained an effect similar to the thirdembodiment of the present invention.

(Fifth Embodiment)

Description will be given of a fifth embodiment of a portable telephoneaccording to the present invention with reference to FIG. 5.

Referring to FIG. 5, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 4.However, a feed/ground point 17 c provided at an end portion of anantenna element 19 is electrically connected to terminals 8 o and 8 s onrespective changeover switches 7 a and 7 c. Feed/ground point 17 c isconnected to terminal 8 o through a filter 20 a a as a first filtertransmitting a current having a first frequency. Furthermore,feed/ground point 17 c is connected to terminal point 8 s through afilter 20 b as a second filter transmitting a current having a secondfrequency. A terminal 8 n electrically connected to a feed source 6 afeeding a current having the first frequency is provided on change-overswitch 7 a. Furthermore, a terminal 8 p grounded to one end portion of aboard 3 is provided on change-over switch 7 a. Switching betweenconnections of terminal 8 o with each of terminals 8 m and 8 p isenabled in change-over switch 7 a.

Furthermore, a terminal 8 q electrically connected to a feed source 6 cfor feeding a current having a second frequency and a terminal 8 rconnected to one end portion of board 3 are provided on change-overswitch 7 c. Switching between connections of terminal 8 s with each ofterminals 8 q and 8 r is enabled in change-over switch 7 c.

Furthermore, a feed/ground point 17 d provided at the other end portionof antenna element 19 is electrically connected terminals 8 x and 8 uprovided on change-over switches 7 b and 7 d. Feed/ground point 17 d isconnected to terminal 8 x through filter 20 a a as a third filtertransmitting a current having the first frequency. Furthermore,feed/ground point 17 d is connected to terminal point 8 u through filter20 b as a fourth filter transmitting a current having the secondfrequency. A terminal 8 y connected to a feed source 6 b for feeding acurrent having the first frequency and a terminal 8 w grounded to theother end portion of board 3 are provided on change-over switch 7 b.Switching between connections of terminal 8 x with each of terminals 8 yand 8 w is enabled in change-over switch 7 b. A terminal 8 v connectedto a feed source 6 d for feeding a current having the second frequencyand a terminal 8 t grounded to the other end portion of board 3 areprovided on change-over switch 7 d. Switching between connections ofterminal 8 u with each of terminals 8 t and 8 v is enabled inchange-over switch 7 d.

With such a construction adopted, not only an effect similar to thefourth embodiment can be achieved, but feed sources 6 a and 6 c feedingcurrents having respective different frequencies can be connected tofeed/ground point 17 c as a first common connection point of the antennaby using filters 20 a and 20 b. Furthermore, by using filters 20 a a and20 b disposed on the right side of FIG. 5, feed sources 6 b and 6 dfeeding currents having respective different frequencies can beconnected to feed/ground point 17 d as a second common connection pointof the antenna, that is since two feed sources 6 a and 6 c can beconnected to the antenna with feed/ground point 17 c and other two feedpoints 6 b and 6 d can be connected to the antenna with feed/groundpoint 17 d, the number of connection points of feed sources with theantenna can be reduced. As a result, a construction of the antenna canbe simplified. Therefore, there can be achieved reduction in size andweight of portable telephone 1.

(Sixth Embodiment)

Description will be given of a sixth embodiment of a portable telephoneaccording to the present invention with reference to FIG. 6.

Referring to FIG. 6, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 3.However, a feed/ground point 17 a of a flat plate antenna 4 iselectrically connected to a terminal 8 i through a first matchingcircuit 21 a. Furthermore, a feed/ground point 17 b of flat plateantenna 4 is connected to a terminal 8 l through a second matchingcircuit 21 b.

With such a construction adopted, not only can an effect similar to thethird embodiment of the present invention is attained, but a fineadjustment of an antenna characteristic can also be achieved using thefirst and second matching circuits 21 a and 21 b.

(Seventh Embodiment)

Description will be given of the seventh embodiment of a portabletelephone according to the present invention with reference to FIG. 7.

Referring to FIG. 7, a portable telephone 1 has a constructionfundamentally similar to the portable telephone shown in FIG. 2.However, in portable telephone 1 shown in FIG. 7, change-over groundpoints 22 a to 22 t are provided at two positions in respective both endportions of a flat plate antenna 4. Change-over ground point 22 a iselectrically connected to a terminal 23 c of a change-over switch 7 a.Furthermore, change-over ground point 22 b is electrically connected toa terminal 23 a of change-over switch 7 a. A terminal 23 b grounded toone end portion of a board 3 is disposed on change-over switch 7 a.Switching between connections of terminal 23 b with each of terminals 23a and 23 c is enabled in change-over switch 7 a.

Moreover, change-over ground point 22 c of flat plate antenna 4 iselectrically connected to a terminal 23 d of a change-over switch 7 b.Change-over ground point 22 d is electrically connected to a terminal 23f of change-over switch 7 b. A terminal 23 e grounded to the other endof board 3 is disposed on change-over switch 7 b. Switching betweenconnections of terminal 23 e with each of terminals 23 d and 23 f isenabled in change-over switch 7 b. Moreover, a feed source 6 can feed acurrent having a first frequency and a current having a second frequencydifferent from the first frequency.

With such a construction adopted, not only can an effect similar to thesecond embodiment of the present invention, but a position of a groundpoint of flat plate 4 can be changed by controlling change-over switch 7a to select one of change-over ground points 22 a and 22 b. As a result,an effective electrical length of flat plate antenna 4 can be changed.Hence, there can be realized portable telephone 1 capable oftransmitting/receiving radio waves having respective differentfrequencies of the first and second frequencies.

(Eighth Embodiment)

In order to confirm a characteristic of a portable telephone accordingto the present invention, the following test was performed. Referring toFIG. 8, a length L1 of a board 3 was 110 mm and a width L2 was 33 mm. Aflat plate antenna 4 of a size of 30 mm in width W1 and 5 mm in heightW2 was mounted on board 3 with a clearance of 5 mm therebetween. Feedpoints 24 a and 24 b between which switching is possible, and which areconnected to feed sources (not shown) were connected to both endportions of flat plate antenna 4. For example, a change-over switch 7 asshown in FIG. 1 can be used as change-over means for feed points 24 aand 24 b.

Note that a direction heading for a region in which flat plate antenna 4is mounted from the bottom portion of board 3 of the figure was used asthe +Z direction (a direction heading for above from below of FIG. 8). Adirection heading for the left from the right was used as the +Ydirection. A direction heading for the front from the back of the sheetof paper of the figure was used as the +X direction.

First of all, referring to FIG. 9, an antenna device shown in FIG. 8 wasplaced on a table 150. At this time, the antenna device was placed suchthat the +Z direction and the +X direction shown in FIG. 8 were almostperpendicular to a vertical direction shown with an arrow mark 140.Hence, the +Y direction assumes a position almost parallel to a verticaldirection. Furthermore, table 150 was rotatable in a direction indicatedwith an arrow mark R.

In such a state where antenna device is placed on table 150, a radiowave having a frequency of 1.5 GHz is radiated from the antenna devicewith a prescribed output. Furthermore, at that time, table 150 wasrotated in the direction indicated with arrow mark R. With such aconstruction adopted, a radio wave as shown with an arrow mark 151 wasradiated from the antenna device. An electric field strength of theradio wave was measured with a measuring antenna 160. As a result,electric field strengths of a vertically polarized wave in a directionindicated with an arrow mark V, and a horizontally polarized wave in adirection indicated with an arrow H were obtained.

Referring to FIG. 10, a dipole antenna 170 was placed on table 150. Indipole antenna 170, a feed point 171 was provided in the centralportion, and feed point 171 was connected to a coaxial cable 172.Coaxial cable 172 was connected to a prescribed wirelessreceive/transmit section. Dipole antenna 170 was installed so as toextend in a direction almost parallel to a vertical direction indicatedwith arrow mark 140. By giving an output similar to the output given toan antenna 2 shown in FIG. 7 to dipole antenna 170 while rotating table150 in the direction indicated by arrow mark R, a radio wave having afrequency of 1.5 GHz was radiated from dipole antenna 170. As a result,a radio wave indicated with an arrow mark 152 was radiated from dipoleantenna 170. The radio wave was a vertically polarized wave having adirection indicated with an arrow mark V. An electric field strength ofthe radio wave was measured with measuring antenna 160.

Referring to FIG. 11, dipole antenna 170 was placed on table 150. Dipoleantenna 170 was installed so as to extend in a direction almostperpendicular to a vertical direction indicated with arrow 140. Feedpoint 171 is provided at the center of dipole antenna 170. Feed point171 was connected to coaxial cable 172. By giving an output similar tothe output given to antenna 2 shown in FIG. 7 to dipole antenna 170while rotating table 150 in the direction indicated with arrow mark R, aradio wave having a frequency of 1.5 GHz and indicated with an arrow 153was radiated from dipole antenna 170. The radio wave was a horizontallypolarized wave having a direction indicated with an arrow mark H. Anelectric field strength of the radio wave was measured with measuringantenna 160.

A radiation pattern of the antenna device according to the presentinvention was obtained based on data measured in the processes shown inFIGS. 9 to 11. The results are shown in FIGS. 12 and 13.

Referring to FIGS. 12 and 13, solid lines 25 and 27 are a gain of avertically polarized wave component of a radio wave radiated from theantenna device shown in FIG. 9 to an electric field strength of avertically polarized wave radiated from dipole antenna 170 in theprocess shown in FIG. 10. The gain was calculated according to thefollowing formula:

(Gain)=20×log₁₀(an electric field strength of a vertically polarizedwave from an antenna device/an electric field strength of a verticallypolarized wave from dipole antenna 170)

In addition, dotted lines 26 and 28 are a gain of a horizontallypolarized wave component of a radio wave radiated from the antennadevice shown in FIG. 9 to an electric field strength of a horizontallypolarized wave radiated from dipole antenna 170 in the process shown inFIG. 11. The gain was calculated according to the following formula:

(Gain)=20×log₁₀(an electric field strength of a horizontally polarizedwave from an antenna device/an electric field strength of a horizontallypolarized wave from dipole antenna 170)

Referring to FIGS. 12 and 13, by switching between feed points 24 a and24 b in the antenna device shown in FIG. 8, it is understood thatradiation patterns are inverted from each other laterally. That is, itis understood that by switching between feed points 24 a and 24 b,polarization and directivity of an antenna can be changed.

As described above, while description is given of the embodiments of thepresent invention, features of the embodiments may be combined in aproper way. The embodiments disclosed this time are given by way ofillustration but should not be taken by way of limitation in allaspects. The scope of the present invention is not shown by the aboveembodiments but by the claims and it is intended that the scope of thepresent invention includes the claims, equivalence of the claims and allmodifications or alterations in the claims.

INDUSTRIAL APPLICABILITY

An antenna device and portable equipment according to the presentinvention can be used in not only a portable telephone, but also in afield of a portable information terminal such as a personal computerhaving a communication function.

What is claimed is:
 1. An antenna device comprising: a conductive boardhaving one end portion and the other end portion opposite the one endportion; a flat plate antenna mounted on said board with a dielectricinterposing therebetween wherein when feeding a current thereto toexcite, a current also flows in said board; first current directionchange means for changing a direction of said current flowing in saidboard to a first direction when exciting said antenna, and located onsaid one end portion of said board; and second current direction changemeans for changing a direction of said current flowing in said board toa second direction different from but intersecting said first directionwhen exciting said antenna, and located on the other end portion of saidboard.
 2. The antenna device according to claim 1, wherein said antennais installed so as to extend from a position on said one end portion ofsaid board to a position on the other end portion of said board, saidfirst current direction change means includes: a first feed means, whichis connected to one portion of said antenna located on said one endportion of said board, for exciting said antenna; and a first feedcontrol means for controlling feed of a current to said antenna fromsaid first feed means, and said second current direction change meansincludes: a second feed means, which is connected to a second portion ofsaid antenna located on the other end portion of said board, forexciting said antenna; and a second feed control means for controllingfeed of a current to said antenna from said second feed means.
 3. Theantenna device according to claim 1, further comprising: a feed meansfor exciting said antenna, wherein said antenna is installed so as toextend from a position on said one end portion of said board to aposition on the other end opposite said one end portion of said board, asaid first current direction change means includes: a first ground meansfor electrically connecting one portion of said antenna located on saidone end portion of said board with one end portion of said board; and afirst ground control means for controlling connection of said firstground means with said antenna, said second current direction changemeans includes: a second ground means for electrically connecting asecond portion of said antenna located on the other end portion of saidboard with the other end portion of said board; and a second groundcontrol means for controlling connection of said second ground meanswith said antenna.
 4. The antenna device according to claim 3, whereinsaid feed means is connected to the central portion of said antenna; insaid first ground means, said one end portion of said board is connectedto said one portion of said antenna at a first ground point of said oneportion of said antenna; and in said second ground means, said other endportion of said board is connected to the second portion of said antennaat a second ground point of the second portion of said antenna; and,said first ground point and said second ground point are located atpositions in bilateral symmetry with respect to the central portion ofsaid antenna.
 5. The antenna device according to claim 1, wherein saidantenna is installed so as to extend from a position on said one endportion of said board to a position on the other end portion oppositesaid one end portion of said board, said first current direction changemeans includes: a first ground means for electrically connecting oneportion of said antenna located on said one end portion of said board tosaid one portion of the board; a first feed means, which is connected tosaid one portion of said antenna located on said one end portion of saidboard, for exciting said antenna; and a first feed ground control meansfor switching between said first ground means and said first feed means,said second current direction change means includes: a second groundmeans for electrically connecting a second portion of said antennalocated on the other end portion of said board to the other end portionof said board; a second feed means, which is connected to said secondportion of said antenna located on the other end portion of said board,for exciting said antenna; and a second feed ground control means forswitching between said second ground means and said second feed means.6. The antenna device according to claim 1, wherein an electrical lengthof said antenna is substantially ¼ times a wavelength of a radio wavethat can be received by said antenna.
 7. The antenna device according toclaim 1, wherein said antenna includes: a first element capable ofreceiving a radio wave having a first frequency; and a second elementcapable of receiving a radio wave having a second frequency differentfrom said first frequency.
 8. The antenna device according to claim 1,wherein said first current direction change means includes: a first feedsource feeding a current having a first frequency for exciting saidantenna; a second feed source feeding a current having a secondfrequency different from said first frequency for exciting said antenna;a first filter transmitting a current having said first frequency; and asecond filter transmitting a current having said second frequency, saidfirst feed source is connected to a first common connection point ofsaid antenna through said first filter and said second feed source isconnected to said first common connection point of said antenna throughsaid second filter, and wherein said second current direction changemeans includes: a third feed source feeding a current having said firstfrequency for exciting said antenna; a fourth feed source feeding acurrent having said second frequency different from said first frequencyfor exciting said antenna; a third filter transmitting a current havingsaid first frequency; and a fourth filter transmitting a current havingsaid second frequency, said third feed source is connected to a secondcommon connection point of said antenna through said third filter andsaid fourth feed source is connected to said second common connectionpoint of said antenna through said fourth filter.
 9. The antenna deviceaccording to claim 1, wherein said antenna includes a part having afunction as a conductive wire for a current fed to said antenna and afunction as a matching element.
 10. The antenna device according toclaim 1, wherein said first current direction change means includes: afirst matching circuit member; and a first feed means electricallyconnected to said antenna through said first matching circuit member andsaid second current direction change means includes: a second matchingcircuit member; and a second feed means electrically connected to saidantenna through said second matching circuit member.
 11. A portableequipment comprising an antenna device according to claim 1.